1. Field of the Invention
The present invention relates to an image forming material, particularly an image forming material on which an image can be easily formed with a high resolution and which is useful as a display material and a pattern formation material, to a color filter master plate suitable for application to a staining method for producing a color filter to be employed in a liquid crystal display device or a solid imaging device and, to a color filter as well.
2. Description of the Related Art
Conventionally, a variety of images forming materials have been used as display materials and pattern forming materials. In general, when they are used for carrying out image formation, a material, e.g., a colored material such as an ink, is imagewise deposited on the surface of a white image receiving material such as a paper medium, or a material, e.g., a nontransparent material such as a pigment, is imagewise deposited on a transparent image receiving material such as a plastic film.
The image formation is carried out by a variety of methods, e.g., by depositing an ink on the image receiving material by inkjet printing, by imagewise coloring a dye precursor by heating a heat-sensitive recording material used for printing by electrostatically causing a colored material to adhere to a surface of the image receiving material and then thermally fixing the material, typically by a copying machine, or the like.
Also, as a method for forming a dense and precise pattern with controlled orientation, for example, Japanese Patent Application Laid-Open (JP-A) No. 2000-247799 proposes a method for producing a functional organic molecular thin film. Dense and precise patterns can be formed according to the method, but in order to write an image pattern, UV exposure through a mask, such as a lithographic film, is required just as in a conventional image forming method using a lithographic printing plate. The process is thus a complicated image forming method.
Further, it is difficult to form an image with a high resolution on an image receiving material with a large surface area or to form an image with a high density on thin-film image receiving material by conventional and general image forming methods.
On the other hand, a variety of methods for forming images directly on image receiving materials from digitized image data without using a medium such as a lithographic film have been recently proposed and have received attention.
While there is an expectation that by employing such digitized image forming methods, it will be possible to form a clear image irrespective of surface area and properties of an image receiving material. No technology capable of stably fixing a nontransparent material or a dye on a desired image receiving material based on the digitized data has been established as of yet.
Next, there are various known methods for producing color filter to be employed in liquid crystal display devices and solid imaging devices including a staining method, an electrodeposition method, a printing method, a pigment dispersing method and the like.
In the staining method a color filter is produced by staining a staining substrate made of natural resin such as gelatin, glue, casein or the like, or synthetic resin such as amine-modified polyvinyl alcohol or the like.
In the electrodeposition method a color filter is produced by forming a predetermined pattern of transparent electrodes and then forming a color image based on the pattern by ionizing resin containing a pigment dissolved or dispersed in a solvent by application of a voltage.
The electrodeposition method requires a photolithographic process which includes a step for forming a film of transparent electrodes for forming the color filter, aside from other than the transparent electrodes for displaying, and an etching step. If a short circuit occurs in that case, line defects are generated resulting in a decrease in production yield. Further, there are problems with this method in that, theoretically, it is difficult to apply the method to, for example, a mosaic arrangement other than a stripe arrangement and the transparent electrodes are difficult to control.
The printing method is a simple method for producing a color filter by printing, such as offset printing, using an ink containing a pigment dispersed in a heat-hardenable resin or a UV-hardenable resin. Since a suitable ink has a high viscosity, filtering is difficult to carry out and defects easily appear in portions where dust or foreign substances are present or where an ink binder causes gelling. There are also problems with respect to printing precision, positioning precision, line width precision, and plane smoothness.
In the pigment dispersion method is a color filter is produced by a photolithographic method using coloring and irradiation sensitive compositions containing pigments dispersed in a variety of photosensitive compositions. This method is suitable for producing a color filter for a large surface with very fine color display since the obtained color filter is stable with respect to light and heat due to use of a pigment and since it has high positioning precision due to patterning by the photolithographic method, and currently, continues to be in the main stream of color filter production methods.
Recently, along with progress toward further fineness, power efficiency of back lights, and a high brightness in a liquid crystal display devices, there is a desire to achieve a higher transmittance and higher contrast for color filters. In the pigment dispersion method, it is essential to make the pigment fine in order to achieve high fineness in the display device, but new problems arise with the achievement of greater fineness including an increase in viscosity of a dispersion and precipitation of the pigment due to aggregation.
JP-A No. 8-6242 discloses a new method requiring no pigment dispersion and carried out by forming an image with dye, which is a molecule dispersion type pigment precursor (latent pigment), and then converting the pigment precursor to a pigment by a chemical method, a thermal method, or a photodecomposition method.
The method is unsatisfactory in that the conversion to the pigment by the chemical method, the thermal method, or the photodecomposition method is insufficient and that the intrinsic properties of the dye are lost due to the conversion. In particular, since a degree of conversion to the pigment differs depending on temperature, there is a problem in that coloring with different hues results depending on a heating temperature, and accordingly, no color filter with sufficiently practical hue stabilization has been obtained as of yet.
In the case of solid imaging devices such as CCD and C-MOS, it has become clear that roughness due to pigment dispersion, which has not been a problem before, affects the performance. With the pigment dispersion method having the above-described problem, and the staining method, using a dye, has received attention recently.
The staining method is a method for producing a color filter by staining a staining substrate comprising a thin film of natural resin such as transparent gelatin, glue, casein or the like, or synthetic resin such as amine-modified polyvinyl alcohol or the like, in a stripe- or mosaic-like pattern (hereinafter referred as to a pattern) with a dye on the surface of a substrate comprising glass or silicone wafer.
The following three methods are known for producing a color filter by staining.    (1) A coloring layer is formed by providing a coating film to be colored on a surface of a substrate, forming a pattern by exposure and development through a mask, and then staining the obtained pattern. After that, a non-colored protective film is formed on the entire surface of the coloring layer and by a similar procedure to that described above, a second coating film to be colored is further formed thereon.
Following that, coloring layers are successively layered as necessary to form coloring layers of the three primary colors, R (red), G (green), and B (blue), of the primary color system or the three primary colors, Y (yellow), M (magenta), and C (cyan) of the complementary color system. In this case, since protective films are disposed on the surface of the respective coloring layers, the filters for the respective colors are not formed in a single plane and thus steps are formed.    (2) A coloring portion is formed by providing a coating film to be colored on a surface of a substrate, forming a positive resist layer thereon, forming a pattern by exposure and development through a mask, staining the coating layer, and separating the positive resist layer. After that, the steps of forming a positive resist layer and successive steps are repeated to separately stain the single coating layer in desired patterns with a plurality of colors.    (3) After a coating film to be colored is formed on a surface of a substrate, patterns formed by exposure and development through a mask are stained to form a coloring layer, and then fixation and stain-preventive treatment is carried out with tannic acid. A second coating to be colored is then formed in a similar manner. Successively, additional coloring layers are formed on the surface of the same substrate.
In the method (1), protective films are required and therefore the coloring layers composing the color filter cannot be formed on a single plane. By the methods (2) and (3), although the respective coloring layers can be formed on a single plane, coating films to be colored and the positive resist have to be applied a plurality of times.
Also, with of these methods, the steps are complicated and rather many steps are required to complete the color filters.
As described above, along with increased demand for higher pixels densities, there is a desire for a color filter which is more easily produced with excellent properties which conventional color filter do not have.